Angle mode area navigation computer

ABSTRACT

Disclosed is an area navigation system which generates course deviation information in terms of angular measurement. The system is compatible with all standard VOR and DME equipment. It comprises a vector computer for computing the &#39;&#39;&#39;&#39;C&#39;&#39;&#39;&#39; vector from a waypoint to an aircraft and from the computer output generates a voltage signal representative of distance and a variable phase signal representative of varying angle. It incorporates an approach mode switch for maintaining an approximately constant maximum angular course width sensitivity in the area of the waypoint.

United States Patent 1191 1111 3,796,867 Abnett et a]. Mar. 12, 1974 [54] ANGLE MODE AREA NAVIGATION 3,534,399 10/1970 Hirsch 235/150.27

COMPUTER 3,643,074 2/1972 Hobbs..... 235/l50.27 3,090,953 5/1963 Brown 235 190 x 1 Inventors: Albert Abnett, Westerville; 3,685,053 8/1972 Kirkpatrick 343/106 R Robert M. Watson, Uniontown, both of Ohio Primary ExaminerMalco1m A. Morrison [73] Assignee: Autech, Inc., Columbus, Ohio Assis t Examiner-Jerry Smith Attorney, Agent, or FirmLeBlanc & Shur [22] Filed: June 6, 1972 [21] Appl. No.1 260,194 [57] ABSTRACT Disclosed is an area navigation system which gener- [52] Cl 333 432 3 53520225 ates course deviation information in terms of angular 5 l 1 Int Cl g measurement. The system is compatible with all standard VCR and DME equipment. It comprises a vector computer for computing the C vector from a waypoint to an aircraft and from the computer output [58] Field of Search 235/1502, 150.26, 150.27, 235/186, 190;343/10,l5,106 R, 107, 112

112 D generates a voltage signal representative of distance d References Cited an a var able phase slgnal representatwe of vary1ng angle. It incorporates an approach mode sw1tch for UNITED STATES PATENTS maintaining an approximately constant maximum an- 3,581,073 5/1971 Visher 235/150.26 gular course width sensitivity in the area of the way- 3,500,4l3 3/1970 Dohogne et a1.

....... 343/107 point.

3,652,837 3/1972 Perkins 235/150.27 3,659,291 4/1972 Anthony 343/106 R X 29 Claims, 17 Drawing Figures 62 as 96 B4 64 7 L.- "c" e 112 VOR PHASE 3 CONVERTER BEAR'NG 98V 120 I02 GENERATOR R V DISPLAY BEARING "c" I 7 B6 RANGE TA RANGE VECTOR sT A 1i0A iii1l A COMPUTER DlSTANCE VECTOR I04 GENERATOR COUPLER PHENIEDM I! M FIG. 4

FILTER ALC / II II C VECTOR COMPUTER VOLTAGE STANDARD VOR VIDEO lwm COMBINING OIRCOIT RNAV VOR

CONVERTER RNAV FIG. 6

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ANGLE MODE AREA NAVIGATION COMPUTER This invention relates to area navigation systems and more particularly to an area navigation computer which presents course deviation information in terms of angular measurement. It is fully compatible with existing VOR and DME equipment and presents information to the aircraft pilot in a conventional VORTAC format.

The concept of area navigation is an outgrowth of the availability of a wide spread network of air navigation aids called VORTACs. These combine the capabilities of standard VHF omni-directional range (VOR) equipment with the tactical air navigation TACAN system to provide radial signals which are utilized on board aircraft to provide azmuth (bearing) and range information for the aircraft with respect to the VORTAC facility. Thus, an aircraft suitably equipped with VOR and DME (distance measuring equipment) receivers can locate its bearing and range relative to a VORTAC station. By reference to chart showing the VORTAC location, the absolute position of the aircraft may readily be ascertained. The resulting information is customarily utilized to maintain a course between a succession of VORTAC facilities along the desired course. Suitable on board indicators show range data and left-right deviation with respect to a selected course to or from the VORTAC. The left-right information is conventionally displayed in terms of the angular deviation of the aircraft from the desired course to the VORTAC.

To alleviate the inevitable overcrowding of established airways between VORTACs, area navigation may be used to pilot a course across country, i.e., off the established airways. Such a course can be along tracks parallel to established airways between VOR- TACs or simply between a series of arbitrary or phantom points, usually referred to as waypoints within a range of succession of VORTAC facilities near the desired course.

In practice, the series of waypoints are defined by the range and bearing to a nearby VORTAC. An on board navigation computer solves the vector triangle defined by the VORTAC to aircraft and VORTAC to waypoint vectors to generate a third vector commonly called a C vector representing the range and azmuth or bearing from the waypoint to the aircraft. This is fully equivalent to the VORTAC to aircraft vector in terms of locating the aircraft, and navigation with respect to the waypoints proceeds as it would with direct reference to the VORTACs themselves. Because a waypoint may be located arbitrarily (but within the range of the reference VORTAC) the pilot is no longer constrained to flight along or near the established airways but instead may fly along any convenient course to his particular destination.

From the above, it may be appreciated that an area navigation system must include a suitable VOR or NAV receiver, and a DME receiver to generate the bearing and range components for the VORTAC to aircraft vector and the area navigation computer must include means to generate the VORTAC to waypoint vector, and equipment to solve the vector triangle to generate the waypoint to aircraft vector. In addition, suitable display equipment must be provided to make the area navigation data conveniently usable by the pi lot.

Complete area navigation systems including all of the foregoing are available from several sources. One such system has become the standard for use in commercial aviation and is a highly effective and useful piece of equipment. However, such equipment is quite expensive and is consequently beyond the means of most general aviation pilots.

Less expensive area navigation systems are available from other sources, but these suffer from several disadvantages. For example, considering all the required components, the systems are still quite costly, whereby pilots typically purchase the required equipment in stages, beginning with the VOR receiver, and then the DME receiver which are usable for standard VOR and VOR-DME navigation. Thus, while the area navigation computers are obtainable separately, computers available from one source are seldom compatible with other system components provided by other suppliers. This may significantly limit a potential purchase in the choice of new equipment. This is a significant consideration since it is estimated that well over one hundred thousand operational aircraft are already equipped with VOR and DME receivers, few of which already have area navigation capabilities. An important feature of the area navigation computer of the present invention is its compatibility with all known VOR and DME equipment.

In order to overcome these and other problems, there is disclosed in assignees copending application Ser. No. 219,992 filed Jan. 24, 1972 in the name of Stephen F. Bean a novel distance mode area navigation computer. The present invention is directed to a generally similar system in which the bearing information is provided in an angular mode instead of in a distance mode. The angular mode presentation possesses several important advantages, not the least of which is the fact that it corresponds to the presentation normally made in conventional VOR or VORTAC navigation with which most airline pilots are already thoroughly familiar. Pilot familiarity with the form of display is a significant safety feature in that aircraft navigational experience with the angular display substantially lessens the possibility of pilot error and risk of accident. Another important advantage resulting from angular presentation of bearing information lies in the fact that the course deviation information becomes more accurate as the waypoint is approached and just at the time when more accuracy is needed.

In the present invention, the area navigation computer is coupled to a conventional VOR receiver for receiving bearing or azmuth information from a VOR- TAC and to a conventional DME receiver for receiving distance or range information from the VORTAC station. Incorporated in the system is a switch so that the pilot at his option may switch over to VORTAC and fly to the VORTAC station in a conventional manner. When the system is manually switched to RNAVa (area navigation angular) the pilot may fly to a waypoint using exactly the same instrument display and visual guides that he would use in flying straight VOR- TAC. The VOR video information containing the bearing between the VORTAC and the aircraft is applied to a C" vector computer. This video signal contains a 30 Hz variable phase sinusoid representing the bearing portion of the A vector between the VORTAC and the aircraft, which variable phase 30 Hz signal constitutes part of the A vector and is hereinafter referred to as the A" phase. Also supplied to the C vector computer is a signal from the DME receiver represent ing the range or distance portion of the A vector. With the aid of maps and a knowledge of the location of the VORTAC station, the aircraft pilot dials into the C vector computer the B vector address which consists of the bearing and distance information defining the 8" vector between the VORTAC station and the selected waypoint. Using the information put into the computer by the pilot defining the known B vector and the bearing and range information from the VOR and DME receivers defining the A vector, the computer solves the vector triangle and produces an electrical output representative of the C vector, i.e.. the vector between the waypoint and the aircraft.

The output from the C" vector computer is a 30 Hz sinusoid having a magnitude representative of the dis tance from the waypoint to the aircraft and a phase angle relative to the VORTAC standard or zero degrees reference (ZDR) indicative of the bearing from the waypoint to the aircraft. The "C" vector output is applied to a distance generator which senses the amplitude of this signal and applies a corresponding distance signal to the range portion of the pilots cockpit display.

The "C" vector computer output is also applied to a C" phase generator which normalizes the C vector magnitude and then combines it with the 9,969 Hz component of the original VOR video signal to produce a reconstituted VOR video having a 30 Hz variable phase sinusoidal component representative of the bearing of the C vector. This signal is applied to a conventional VOR converter and finally to a course deviation indicator (CDI) which produces an angular display to the pilot of bearing information.

Additional important features of the present invention include the fact that the reconstituted VOR video or RNAVa" signal containing the C phase information may be applied directly to a conventional automatic VOR radio magnetic indicator (RMl) to display heading data and not just bearing. In addition the area navigation system of the present invention includes an approach mode switch for producing an increased and substantially constant angular course width in the course deviation indicator (CDI) in the area of the waypoint. This feature is particularly advantageous in those situations in which the pilot desires to land at or near the waypoint.

It is therefore one object of the present invention to provide an improved area navigation system.

Another object of the present invention is to provide an improved area navigation system whicn incorporates an angular display of bearing information.

Another object of the present invention is to provide an improved on board area navigation computer.

Another object of the present invention is to provide an area navigation computer which is completely compatible with existing VCR and DME navigation receivers.

Another object of the present invention is to provide an area navigation system in which the pilot can fly from waypoint to waypoint in the same manner that he would conventionally fly from VORTAC station to VORTAC station with conventional VCR and DME receiving equipment.

Another object of the present invention is to provide on board area navigation display which provides the same information in the same format for a waypoint as is supplied by conventional equipment for a VORTAC station.

Another object of the present invention is to provide an improved area navigation computer which produces a reconstituted VOR video signal having essentially the same properties representative of the C vector as the conventional VOR signal has for the A vector.

Another object of the present invention is to provide an improved area navigation system which through a simple flip of the switch may be converted from straight VORTAC to area navigation and vice versa.

Another object of the present invention is to provide an angular mode area navigation system having an approach mode switch for establishing a substantially constant course width in a course deviation indicator.

Another object of the invention is to provide for use of more than one VOR receiver and/or CDI and VCR converter.

These and further objects and advantages of the invention will be more apparent upon reference to the following specification, claims and appended drawings wherein:

FIG. 1 is a vector diagram useful in the understanding of the underlying concepts of area navigation;

FIG. 2 is a simplified block diagram of an angle mode area navigation system in accordance with the present invention;

FIG. 3 illustrates the wave form of a conventional VOR video signal as it appears at the output of a conventional VOR receiver;

FIG. 4 is a more detailed block diagram illustrating some of the components of the C" phase generator of FIG. 2;

FIGS. 5A and 5B, taken together, show a detailed block diagram of the area navigation system of the present invention as illustrated in FIG. 2;

FIG. 6 is a block diagram illustrating CDI damping and showing the approach mode switch forming a part of the present invention;

FIGS. 7A, 7B and 7C, taken together, constitute a detailed circuit diagram of the VCR-DME portion of the block diagram of FIGS. 5A and 58;

FIGS. 8A, 8B, 8C, and 8D, taken together, constitute a detailed circuit diagram of the computer portion of the block diagram of FIGS. 5A and 5B; and

FIGS. 9A, 9B and 9C, taken together, constitute a detailed circuit diagram of the digital portion of the block diagram of FIGS. 5A and 58.

Referring to the drawings, in FIG. 1 there is illustrated a VORTAC station 10 and an aircraft 12 located in an arbitrary position with respect to station 10. The position of the aircraft with respect to the VORTAC is ordinarily defined in terms of a vectorAhaving a magnitude /A/ and an azmuth or bearing (with respect to North) of gin. (Conventionally, vectors emanating from a VORTAC are termed radials, and the A vector in FIG. 1 coincides with the d),, radial of VORTAC 10. The inverse of the angle (11, 4),, is the aircraft bearing to the VORTAC.)

In conventional VOR navigation the magnitude /A/ and the angle qb are computed, and utilized to lo: cate the aircraFrelative to the VOR TAC and relative to a selected course, i.e., a desired bearing of approach toward the VORTAC. A left-right course deviation indicator (CDI) provides a measure of how many degrees to the left or right the aircraft bearing must be changed to intercept the desired course. A to-from indicator is normally provided as a part of the course deviation indicator. The to indication is given if the course deviation angle (i.e., desired bearing minus actual bearing) is within plus or minus 90. The from indication is given in the course deviation angle is more than 90 or less than minus 90. The dashed line 14 in FIG. 1 represents the to-from boundary assuming vector Kin fact to be the selected course.

For area navigation the pilot establishes a succession of arbitrary landmarks, such as that denoted 30, and commonly called waypoints. Waypoint 30 has a known bearing (1),; and a range /B/ with respect to a VORTAC such as in its vicinity, thereby defining the vector l? from the VORTAC to the waypoint. The triangle defined by vectors Kand B includes a third side Gdefining an azmuth angle (b and a range /C/ of the aircraft with respect to the waypoint. Since the components of the vector Kare determined by the incoming VOR and DME data, and since the components of the vectorE may be determined for a selected waypoint from a suitable navigational chart, theC ctor can be determined by the vector subtraction A B. Once this is done, the navigato r using an area navigation system may treat the vector C in precisely the same manner as the navigator using standard VOR/DME techniques would treat the vector A.

In particular, a selected track 32, analogous to the selected course mentioned above, may be defined as the desired bearing of the aircraft as it approaches the waypoint, and a track deviation angle (1) computed as the difference between the actual bearing of the aircraft from the waypoint I8O+ and its desired bearing (1) on the selected track, i.e., (15 180 dJ qb Then having measured (actually computed) the range /C/, this range can be displayed as a distance on an appropriate indicator, or this distance may be displayed on an existing indicator already present which otherwise would be displaying DME distance from the V/ORTAC. The angular quantity 1 1; is displayed on a conventional CDI (course deviation indicator). This indicator is a left-right indicating the course deviation in degrees and as in conventional VOR navigation a to-from indicator is used to show whether the aircraft is more or less 90 off the selected track. (See line 34 in FIG. 1.

The aircraft may now be flown from waypoint to waypoint without need to follow crowded airways between VORTACs, thereby improving flight safety and often reducing flight time by allowing selection of a direct route to a destination.

The apparatus of the present invention utilizes the above-described concepts of area navigation in a highly advantageous manner. The essential features of one preferred embodiment of the present invention are illustrated in the block diagram of FIG. 2.

Data from which the vector A is generated is received from a nearby VORTAC by a DME receiver 40 and a VOR or NAV receiver 42. In accordance with an important feature of this invention, receivers 40 and 42 are conventional units available from a variety of sources, and are often already present in the aircraft for use in normal VOR/DME navigation before the owner decides to add the area navigation capability. Such compatibility can significantly reduce the cost of installation, particularly since replacement of a costly receiver, navigation converter and/or display is not necessary and also allows a wide range of equipment selection for a user fitting out an aircraft with a complete installation.

As is well known, the tactical air navigation (TA- CAN) portion of a conventional VORTAC station incorporates a transponder which processes a pulse signal from the DME receiver 40 of FIG. 2 so as to indicate the distance from the VORTAC station to the aircraft. At the same time the VHF omni-directional range (VOR) portion of the VORTAC station transmits a composite bearing signal having a carrier frequency somewhere in the 108.0 117.95 mHz band. The VOR carrier is removed in the VOR receiver 42 so that the VOR output on lead 44 in FIG. 2 is a composite bearing signal of the type illustrated in FIG. 3 and commonly referred to as a VOR video. The VOR video 46 illustrated in FIG. 3 comprises a subcarrier 48 having a frequency of 9,960 Hz. The 9,960 Hz subcarrier is received superimposed on a 30 Hz sine wave as indicated in FIG. 3 by the wave envelope 50. This 30 HZ signal component as produced by the VOR receiver 42 of FIG. 2 is of variable phase depending on the position of the aircraft relative to the VORTAC station and is caused by the rotation of the VORTAC station antenna. The 9,960 Hz subcarrier 48 is also frequency modulated as indicated by the increased spacing in FIG. 3 at 52. This frequency modulation is also at a frequency of 30 Hz and constitutes the reference phase or zero degree reference (ZDR) of the VOR video. When the aircraft is due North of the VORTAC station the two 30 Hz sine waves are exactly in phase. The amount by which the amplitude modulating sine wave is out-ofphase with the frequency modulating ZDR is an indication of the bearing of the aircraft from the VORTAC.

Referring again to FIG. 2, the VOR video on the lead 44 may be supplied directly by way of a lead 54 to the VOR terminal 56 of a manually-operated switch 58. When the movable contact 60 of switch 58 engages VOR terminal 56 the VOR video is supplied directly to a conventional VOR converter 62 and from there by way of a lead 64 to the bearing indicator of the cockpit display generally indicated at 66. Switch 58 is preferably ganged as indicated by the dash line 68 with a second switch 70 having a movable contact 72. When movable contact 60 of switch 58 engages VOR terminal 56, movable contact 72 of switch 70 engages a DME terminal 74, so that DME receiver 40 is connected through distance circuit (DME) 76 by way of a lead 78 to the range portion of the cockpit display 66. Display 66 may be of any conventional construction including the type which provides both bearing and range information for ready viewing by the pilot in the aircraft cockpit. Alternatively the bearing data can be displayed on a conventional CD1 or HSI and the range (to the waypoint) displayed on an indicator separate from that showing DME distance. In such an arrangement the pilot will have both DME distance (to the VOR-' TAC) and waypoint range displayed simultaneously.

The position of movable switch contacts 60 and 72 in FIG. 2 is the normal position of the contacts and is used for straight VOR/DME or straight VORTAC navigation. In order to provide an area navigation capability, movable contacts 60 and 72 are moved by the pilot to the respective RNAVa (area navigation angular) terminals 80 and 82. This movement of the switch contacts connects the VOR converter 62 to the output of a C phase generator 84 and at the same time connects the range display to the output of a distance generator 86.

As will be recalled in connection with the description of FIG. 1, the vector from the VORTAC station to the aircraft is commonly called the A vector; the vector from the VORTAC station to the waypoint is commonly called the B vector; and the vector from the waypoint to the aircraft is commonly called the C vector. The distance information for the A vector is supplied from DME receiver 40 through a coupler 88 to the range input of a C" vector computer 90. Coupler 88 converts the pulse output of the DME receiver 40 into a signal on lead 92 so that it may be accepted by computer 90. Bearing information for the A vector incorporated in the composite VOR video is supplied from the output of VOR receiver 42 by way of lead 44 and additional leads 94 and 96 to the bearing input of the C vector computer 90. The B vector information is supplied to C vector computer 90 by way of a lead 98 from a waypoint selector 100. Using available navigation charts, the pilot manually dials into waypoint selector 100 the necessary range and bearing information for the B vector and this is supplied as a B vector address from waypoint selector 100 by way of lead 98 to C vector computer 90. Waypoint selector 100 may be of the type shown and described in assignees abovementioned co-pending application Ser. No. 219,992, filed Jan. 24, 1972, and supplies over lead 98 a 30 Hz since wave having a magnitude proportional to /B/ and a phase relative to the ZDR representative of qb Computer 90 produces a pair of output signals on leads 102 and 104, both of which are 30 Hz sine waves having a magnitude proportional to /C/ and a phase relative to ZDR indicative of (b This signal is supplied over lead 104 to the distance generator 86 which detects the magnitude of the C vector output from computer 90 and supplies a voltage signal to the range portion of the display proportional to the magnitude of the C vector signal on lead 104. The C vector signal is also supplied by a lead 102 to the input ofC" phase generator 84. In addition to the C vector signal, C phase generator 84 also receives the VOR video from VOR converter 42 by way of leads 44, 94, and additional lead 106, as well as a DC reference voltage from voltage standard source 108 by way oflead 110. The C vector signal on lead 102 is normalized, i.e., given a constant amplitude in C phase generator 84, in conjunction with the reference voltage from source 108, and is then combined in the C phase generator 84 with a portion of the 9,960 Hz component of the VOR video to produce a reconstructed VOR video at its output on lead 112 which is in all respects identical to the original VOR video with the exception that the phase of the 30 H2 amplitude modulating sinesoid is now representative of the C vector, i.e., rather than (154. This reconstructed composite video on lead 112 is supplied through switch 58 to the VOR converter 62 and finally to the bearing portion of the cockpit display 66, where it is displayed in exactly the same manner as in straight VOR. The difference is that the course deviation displayed in display 66 is with respect to the C vector instead of the A vector.

FIG. 4 is a more detailed block diagram showing some of the major components of the C phase generator 84 of FIG. 2. In FIG. 4 like parts bear like reference numerals. The C vector signal on lead 102 is supplied from C vector computer 90 to an automatic level control (ALC) circuit 1 14 which produces a C phase sinusoid on its output lead 116 having a substantially constant amplitude as determined by the reference voltage from standard 108. ALC circuit 114 is an automatic gain control circuit for stabilizing the level of the C phase signal on lead 116. The VOR video on lead 106 is applied to a 30 Hz AM filter 118 which removes the amplitude modulation at 30 Hz from the VOR video. This amplitude modulation is reintroduced in combining circuit 120 in which the amplitude modulation representative of the A phase removed by filter 118 is replaced by amplitude modulation representative of the C phase as applied to the combining circuit 120 over lead 1 16. The resulting output on the lead 1 12 is a reconstructed VOR video which is in all respects identical to the original VOR video with the exception that the 30 Hz A phase amplitude modulating signal has been replaced by a similar signal having the phase of the C vector.

FIGS. 5A and 5B taken together constitute a more detailed block diagram of the area navigation system of FIGS. 2 and 4 and like parts in FIGS. 5A and 5B bear like reference numerals. FIGS. 5A and 5B illustrate only the area navigation portion of the system, it being understood that the VOR and DME sections are of conventional construction as illustrated in FIG. 2.

Referring to FIGS. 5A and 5B, the DME receiver 40 is of conventional construction and produces outputs on three different leads, namely a suppression pulse output on lead 122, a range memory pulse on lead 124, and a memory pulse on lead 126 in'a well known manner. These are supplied to a signal conditioner 128. This signal conditioner may be separate as illustrated or may be incorporated in the conventional DME receiver 40. The output from the signal conditioner 128 is a series of pulses as indicated at 130 with the pulse width of each pulse indicative of the range from the VOR- TAC station to the aircraft. These pulses are applied by way of a lead 132 to a DME lock loss detector 134 forming part of a diagnostic circuit as more fully described below and by way of a lead 136 to a digital-toanalog converter 138. Converter 138 produces at its output an analog signal on lead 92 which is applied to the input of a C vector summation filter 140, forming the C vector computer 90. FIGS. 5A and SB show VOR receiver No. 1 at 42 and a second VCR receiver No. 2 at 42. This is to illustrate that the system of the present invention is fully compatible with different types of VOR or NAV receivers, which are not all standardized and which may have different output characteristics. A switch 142 is illustrated for connection to one or the other VOR receivers but it is understood that only a single VOR receiver is used at any given time and if compatibility with more than one VOR is not desired the switch may be eliminated. The output from the VOR is applied through switch 142 to a level and phase selector 144 which selects the level and hase of its output signal in accordance with the position of a switch 146 which is, again, dependent upon whether the system is connected to a VOR receiver No. 1 or VOR receiver No. 2. If this selectability is not desired switch 146 may be replaced by a jumper wire. From the level and phase selector 144 the VOR video signal passes through a buffer 148 and automatic level control 150 (ALC) to a limiting FM detector 152. Detector 152 detects the FM signal on the VOR video which is a 30 Hz reference phase signal and applies this through a 30 Hz sine wave filter 154, a squarer 156, and a pulse former 158 to produce a very accurate se- 

1. An angle mode area navigation system comprising a first input terminal for receiving station-to-aircraft vector angle information, a second input terminal for receiving station-toaircraft vector magnitude information, a waypoint-to-aircraft vector computer coupled to said first and second input terminals, a station-to-waypoint vector generator coupled to said computer whereby said computer produces at its output an electrical signal representative of the corresponding waypoint-to-aircraft vector, a distance generator coupled to the output of said computer for developing a distance display signal from said computer output, and an angle generator coupled to the output of said computer for developing an angle display signal from said computer output, said angle generator generating a VOR video signal with information representative of the angle of said waypoint-toaircraft vector for application to a VOR converter.
 2. A system according to claim 1, wherein said waypoint-to-aircraft vector computer is an analog computer.
 3. A system according to claim 2, wherein said computer is a sine wave summation filter.
 4. A system according to claim 1, wherein said VOR video signal comprises a 9,960 Hz subcarrier amplitude modulated by a 30 Hz sine wave having a phase indicative of the angle of said waypoint-to-aircraft vector.
 5. A system according to claim 4, wherein said VOR video subcarrier is frequency modulated by a 30 Hz reference phase sine wave.
 6. A system according to claim 1, wherein said angle generator comprises an automatic level control circuit coupled to the output of said comPuter, a combining circuit coupled to the output of said automatic level control circuit, and means coupling said combining circuit to said first input terminal.
 7. A system according to claim 6, wherein said coupling means comprises a high pass filter for passing a frequency modulated VOR video subcarrier.
 8. A system according to claim 7, wherein said automatic level control circuit includes automatic gain control.
 9. An angle mode area navigation system comprising a VOR input terminal for receiving A vector angle information, a DME input terminal for receiving A vector magnitude information, a C vector computer coupled to said VOR and DME input terminals, a B vector signal generator coupled to said computer whereby said computer produces at its output a signal representative of the C vector corresponding to said A AND B vectors, said C vector signal having an amplitude representative of the magnitude of said C vector and a phase representative of the angle of said C vector, first means coupled to the output of said computer for developing a distance display signal proportional to the magnitude of said C vector signal, and second means coupled to the output of said computer for developing an angular display signal proportional to the phase of said C vector signal, said C vector signal comprising a 30 Hz sine wave, said second means comprising a combining circuit for combining a 30 Hz sine wave signal possessing the phase of said C vector signal with a 9,960 Hz signal having a reference phase.
 10. A system according to claim 9 wherein said first means comprises a peak detector for sensing the magnitude of said 30 Hz sine wave.
 11. A system according to claim 9, including means for coupling the output of said combining circuit to a VOR converter.
 12. A system according to claim 9, including a VOR receiver coupled to said VOR input terminal, a DME receiver coupled to said DME input terminal, a VOR converter coupled to the output of said second means, and a digital range display coupled to the output of said first means.
 13. A system according to claim 12, including an angular bearing display coupled to the output of said VOR converter.
 14. A system according to claim 13, wherein said digital range display comprises a plurality of electro-optical display elements.
 15. A system according to claim 14, wherein said elements are arranged in a 7-bar segment array.
 16. A system according to claim 13, wherein said digital range display comprises a meter for displaying range.
 17. A system according to claim 13, wherein said angular bearing display comprises a course deviation indicator.
 18. A system according to claim 13, wherein said angular bearing display comprises a radio magnetic indicator.
 19. An angle mode area navigation system comprising a VOR receiver, a DME receiver, a C vector computer, means coupling said receivers to the input of said computer, a way point selector coupled to the input of said computer, a VOR video signal generator coupled to the output of said computer, a VOR converter coupled to the output of said video signal generator, and a CDI coupled to the output of said converter.
 20. A system according to claim 19, including a damping capacitor coupled across the input of said CDI.
 21. A system according to claim 19, including a range indicator coupled to the output of said computer.
 22. A system according to claim 21, including first switch means between said VOR receiver and said CDI for selectively bypassing said C vector computer, and second switch means between said DME receiver and said range indicator for selectively bypassing said C vector computer.
 23. A system according to claim 22, wherein said first and second switch means are ganged together.
 24. A system according to claim 21, including a variable resistor, and approach mode switch means carried by said range indicator for coupling said variable resistor across the input of said CDI.
 25. A system according to claim 24, wherein said resistor provides a substantially constant maximum angular sensitivity for said CDI.
 26. A system according to claim 25, wherein said sensitivity is approximately + or - 30*.
 27. A system according to claim 21, wherein said range indicator has at least one diagnostic light for indicating loss of a signal in the system.
 28. A system according to claim 27, including means coupled to said range indicator for blanking its display when said diagnostic light is energized.
 29. A system according to claim 27, wherein said range indicator includes a DME signal loss light, a VOR signal loss light and a DMW overrange light. 